Raman spectroscopy study of ZnO-based ceramic films fabricated by novel sol–gel process

The ZnO-based ceramic films doped with different dopants were prepared by a novel sol–gel process. The phase composition of the films was determined via X-ray diffraction analysis. The influence of the dopants on the residual stress, carrier concentration and the secondary phases was studied by means of Raman spectroscopy. Raman spectra show that the E2 phonon frequency shifts 3–6 cm−1 to lower wavenumbers, whereas the A1(LO) mode shifts 3.2–6.1 cm−1 to higher wavenumbers when the films were doped with Bi2O3, Sb2O3, MnO, Cr2O3, Y2O3 and Al2O3, indicating that both the tensile residual stress and the free carrier concentration were increased with doping. The larger stress is considered to originate from the lattice distortion, which was caused by the substitution of the doping ions for Zn2+, and the lattice mismatch between the ZnO crystals and the interfacial phases. The secondary phases were affected markedly by both Y2O3 and Al2O3. The intensity and the position of Raman bands of Zn7Sb2O12 and ZnCr2O4 phases changed obviously. The films showed remarkable nonlinear voltage–current characteristics, but the nonlinear coefficient of the films decreased evidently as the addition of Y2O3 or Al2O3.